Laser Scanning



Introduction

This page is dedicated to the Laser Scanning method used at Iowa State University. The main goal of this method is to measure the height of a stave core by using a high resolution camera and a laser. In order to be able to scan the full length of the stave core, a linear stage is used in the setup. There are two main experiments:

  • Pressurized Test: The goal of this test is to detect flaws between the facing and the honeycomb structure in the stave cores. To achieve this, the stave core is scanned with an internal pressure of 5 PSI and then compare with a scan without internal pressure. The dry nitrogen injected in the core will create bumps in the surface that will be detected with the laser scan. Flaws between the foam and the facing are also possible to detect, but between pipe and facing not.

  • Bending Test: The goal of this test is to simulate the supporting structure where the stave core will be held in the detector, and measure the maximum bending of the stave core.

Equipment & Installation

The main setup consists of six fundamental parts:

  1. High Resolution Camera and Filter.
  2. Laser.
  3. Linear Stage.
  4. Optical Bench.
  5. Laser Line Detector Code (LabVIEW).
  6. Pressurizing System.

Extensive and detailed information about every component of the equipment including their manuals, documentation and how to set them up can be found in Equipment and Installation.

Experiment

Description

The main purpose of the experiment is to measure the height of an object's surface. This is achieved by a laser which is located above the object and projects five lines on top of its surface. The lines are observed by a high-resolution camera located at a 45˚ angle with respect to the laser. For convenience, ignore all lines but one; if this laser line is projected in a non-flat surface, the camera will not observe a smooth line, but one with the shape of the height of the object's surface. Once the experiment has been calibrated carefully, a scale factor between the pattern registered by the camera and the actual height of the surface can be established. In the experiment, this process is done for all five lines which are separated five millimeters apart. A linear stage, perpendicular to the laser lines and parallel to the length of the object, is used to move the camera and the laser every one millimeter until the full scan of the object is completed.

The data recorded, originally in an Excel file, is converted into a ROOT tree to be used for both of the two experiments. For the case of the bending test, the data is plot in a three dimension surface plot. In the case of the pressurized test, an automatic software written in ROOT looks at the data, and finds all possible flaws and classify them. Information about every step of this experiment can be found in the next several sections.

Calibration

As mentioned above, the measurement of the scale factor is crucial to the correct measurement of the object's height. However, it is not the only calibration needed for this experiment. For example, a correct alignment of the camera, the linear stage, the laser and the stave core is needed. A detailed information on how to calibrate the setup is explained here.

Laser Line Detector Code

The experiment is controlled by a LabVIEW code and has two major functions. First, it talks to all the equipment in the experiment, and synchronize them in order to have a successful scan. Second, it finds the laser lines in the field of view of the camera, converts the difference in the actual height, and write the data into an excel file. A detailed information about this code can be found in the page Laser Line Detector, where the code's documentation is found, but also information in how to run a scan, trouble-shooting and more.

Plotting in ROOT

The data output from the laser scanning method is written into Excel files. To facilitate the manipulation and the analysis of the data, it needs to be converted into a ntuple to be read in ROOT. Detailed information on how to do this conversion, and how to make preliminary plots of the scans can be found here.

Flaw Detector Code

Progress & Results

Major updates:
-- CarlosMiguelVergelInfante - 2017-02-14

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Topic revision: r8 - 2017-03-30 - CarlosMiguelVergelInfante
 
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